Plaster of Paris casts have been in use to immobilize body members or limbs for some time. In recent years, the plaster of Paris bandages have been supplemented and, to some extent, superseded by synthetic casting tapes or bandages which employ polymeric materials on a substrate. The polymeric materials are of the type that have been cured by exposure to ultra violet light or which would cure when reacted with water. Examples of the ultra violet light cured cast can be found in U.S. Pat. No. 3,881,473. More recently, water-cured or water-reactive polyurethane compositions have been used in forming orthopedic casts and the polyurethane compositions have largely supplanted other polymeric synthetic casting materials. The polyurethane casting materials are of the type which are disclosed in U.S. Pat. Nos. 4,376,438 and 4,411,262.
The fibrous substrate used in the synthetic casting tapes may be made from any natural or synthetic fiber including a fiberglass material. The fiberglass materials offer advantages in terms of strength of the finished cast when compared to other fibers and various constructions of fiberglass fabrics have been used for the substrates for synthetic casting tapes. The patents mentioned above disclose the use of different fiberglass materials as the substrate for casting tapes. In addition, U.S. Pat. Nos. 3,686,725, 3,787,272 and 3,882,857 disclose specific fiberglass materials, or the treatment of fiberglass materials, to produce fiberglass substrates which are particularly suitable for use in orthopedic casts.
U.S. Pat. No. 4,323,061 discloses a cast substrate made from a combination of glass fibers and a second fiber such as cotton, flax, rayon, wool, acrylic resin, nylon, polytetrafluoroethylene or polyester. The purpose of the second fiber in the substrate is to hold the curable resin on the substrate.
U.S. Pat. No. 3,332,416 discloses a plaster of Paris cast bandage with a woven substrate made with a combination of elastic and inelastic fibers.
U.S. Pat. No. 4,609,578 discloses a fiberglass substrate for casting tapes which has an extensibility of at least 20% and up to 25% to 35%. The fiberglass substrate is heat-set to prevent fraying. Care must be taken when handling of the fabric after knitting and before and after heat treatment to avoid applying undue tension to the fabric which would distort the knots and loops, i.e. stretch the fabric, and permanently lose some of the stretch of the fabric.
U.S. Pat. No. 4,668,563 discloses a cast substrate made from a combination of glass fibers and an elastomeric highly extensible fiber. The substrate has a stretch of from 40 to 200%. The elastomeric fiber is selected or is treated to insure that it is compatible with the water curable polyurethane prepolymer employed in the casting tape. Although the conformability of the tape disclosed is excellent, the presence of the elastomeric fiber in the substrate can cause storage stability or shelf life problems or add cost to the product because of the treatment of the elastomeric fiber that is required to insure longer shelf life. The presence of the elastomeric fiber in the finished product also necessitates a secondary process step, i.e. coating the fabric with a binder, to reduce fraying or ravel.